A large second-order nonlinearity [chi((2)) 1 pm/V 0.2 chi((2)) (22) for LiNbO(3)] is induced in the near-surface ( 4 microm) region of commercial fused-silica optical flats by a temperature (250-325 degrees C) and electric-field (E ~ 5 x 10(4) V/cm) poling process. Once formed, the nonlinearity, which is roughly 10(3)-10(4) times larger than that found in fiber second-harmonic experiments, is extremely stable at room temperature and laboratory ambient. The nonlinearity can be cycled by repeated depoling (temperature only) and repoling (temperature and electric field) processes without history effects. Possible mechanisms, including nonlinear moieties and electric-field-induced second-order nonlinearities, are discussed.

Measurement of vector correlations in molecular scattering is an indispensable tool for mapping out interaction potentials. In a coexpanded supersonic beam, we have studied the rotationally inelastic process wherein deuterium hydride (HD) ( = 1, = 2) collides with molecular deuterium (D) to form HD ( = 1, = 1), where and are the vibrational and rotational quantum numbers, respectively. HD ( = 1, = 2) was prepared by Stark-induced adiabatic Raman passage, with its bond axis aligned preferentially parallel or perpendicular to the lab-fixed relative velocity. The coexpansion brought the collision temperature down to 1 kelvin, restricting scattering to s and p partial waves. Scattering angular distributions showed a dramatic stereodynamic preference (~3:1) for perpendicular versus parallel alignment. The four-vector correlation measured between the initial and final velocities and the initial and final rotational angular momentum vectors of HD provides insight into the strong anisotropic forces present in the collision process.

Molecular interactions are best probed by scattering experiments. Interpretation of these studies has been limited by lack of control over the quantum states of the incoming collision partners. We report here the rotationally inelastic collisions of quantum-state prepared deuterium hydride (HD) with H and D using a method that provides an improved control over the input states. HD was coexpanded with its partner in a single supersonic beam, which reduced the collision temperature to 0-5 K, and thereby restricted the involved incoming partial waves to s and p. By preparing HD with its bond axis preferentially aligned parallel and perpendicular to the relative velocity of the colliding partners, we observed that the rotational relaxation of HD depends strongly on the initial bond-axis orientation. We developed a partial-wave analysis that conclusively demonstrates that the scattering mechanism involves the exchange of internal angular momentum between the colliding partners. The striking differences between H/HD and D/HD scattering suggest the presence of anisotropically sensitive resonances.

We propose a method based on Stark-induced adiabatic Raman passage (SARP) for preparing vibrationally excited molecules with known orientation and alignment for future dynamical stereochemistry studies. This method utilizes the (J, M)-state dependent dynamic Stark shifts of rovibrational levels induced by delayed but overlapping pump and Stokes pulses of unequal intensities. Under collision-free conditions, our calculations show that we can achieve complete population transfer to an excited vibrational level (v > 0) of the H(2) molecule in its ground electronic state. Specifically, the H(2) (v = 1, J = 2, M = 0) level can be prepared with complete population transfer from the (v = 0, J = 0, M = 0) level using the S(0) branch of the Raman transition with visible pump and Stoke laser pulses, each polarized parallel to the z axis (uniaxial π-π Raman pumping). Similarly, H(2) (v = 1, J = 2, M = ±2) can be prepared using SARP with a left circularly polarized pump and a right circularly (or vice versa) polarized Stokes wave propagating along the z axis (σ(±)-σ(∓) Raman pumping). This technique requires phase coherent nanosecond pulses with unequal intensity between the pump and the Stokes pulses, one being four or more times greater than the other. A peak intensity of ~16 GW/cm(2) for the stronger pulse is required to generate the desirable sweep of the Raman resonance frequency. These conditions may be fulfilled using red and green laser pulses with the duration of a few nanoseconds and optical energies of ~12 and 60 mJ within a focused beam of diameter ~0.25 mm. Additionally, complete population transfer to the v = 4 vibrational level is predicted to be possible using SARP with a 355-nm pump and a near infrared Stokes laser with accessible pulse energies.

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